The elephants are returning in growing numbers to southeast Angola, where thousands of the animals were massacred during the country's protracted civil war, said Chase, who heads the nonprofit conservation group Elephants Without Borders.

The region was headquarters for Jonas Savimbi's rebel UNITA movement, which is reported to have sold ivory to pay for weapons.

Since the end of the war in 2002, elephants have begun to go back to the Luiana Partial Reserve in Angola's sparsely populated Cuando Cubango province that borders southwest Zambia and Namibia (see Africa map).

Chase said that when the initial migration began a number of elephants had their trunks and legs blown off by mines, condemning the animals to agonizing deaths. But the elephants that followed since have avoided those areas.

"I don't know if elephants have 'learned' to avoid land mines, but my limited observations suggest they might have," he said.

"Once I overlay the movements of our five satellite-collared elephants with the location of [the known] mine fields, it would appear that they were avoiding these areas."

Evidence that elephants are avoiding the danger zones is supported by his team's observations on the ground, he added.

"We have not seen any evidence of elephants being blown up or injured by land mine explosions in the three years we have been working in this area," he said.

"Incidents of elephants being injured or killed by land mines used to happen often when elephants were chased over these areas by people."